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Chapter 7
The Discovery of Cells
Cells
 The basic unit of living organisms
The Cell Theory
 Robert Hooke in the 1600s observed cork under a
microscope and named the structures he saw cells
 Many scientists then studied cells. Their work is
summarized in the cell theory:
o All organisms are made up of one or more cells
o The cell is the basic unit of structure and
organization of organisms
o All cells come from preexisting cells
Types of microscopes
 Compound light microscopes: use lenses to magnify
objects up to 1500 times
 Electron microscope: uses a beam of electrons to
magnify objects up to 500,000 times
Two basic cell types
 All cells have organelles: specialized structures in a cell
with a specific function
1. Prokaryotic cells: have no membrane-bound organelles
or nucleus.
 example: bacteria
2. Eukaryotic cells: have membrane-bound organelles
and a nucleus
 examples: plant and animal cells fungus and
protista
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Types of Eukaryotic Cells
 Plant cells
o Tend to be square or rectangular
o Examples: Trees, flowers, vegetables
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 Animal cells
o Tend to be round
o Examples: Animals, insects, humans
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Organelles in eukaryotic cells
Organelle
Function
Name
Plasma (Cell) Allows materials to move in
membrane
and out of cell. Composed of
lipids and proteins
Cytoplasm
clear jelly inside a cell
Ribosome
Makes proteins : most
numerous
Endoplasmic
reticulum (ER)
Golgi
apparatus
Chemical reactions.
Transports proteins
Modifies proteins and
transports. Puts proteins into
sacs called vesicles
Mitochondrion Makes usable energy for the
cell from carbohydrates.
Have inner folds called
cristae where ATP is made.
Nucleus
Cells control center that
contains the DNA. Holds
information for making
proteins.
Nucleolus
Inside the nucleus;
Makes ribosomes
Found in…
Plant & animal
cells
Plant & animal
cells
Plant & animal
cells
Plant & animal
cells
Plant & animal
cells
Plant & animal
cells
Plant & animal
cells
Plant & animal
cells
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Vacuole
Stores food, water, and
waste. Very large in plants.
Plant & animal
cells
Cytoskeleton
network of rods that
maintains the cell’s shape
made up of microtubules and
microfilaments
Supports and protects the
cell. Made of cellulose
(carbohydrate)
Plant & animal
cells
Contains green chlorophyll
pigment which captures
sunlight to produce food
(photosynthesis)
Digests food particles, old
organelles, bacteria, and
viruses. Also called suicide
sacs.
Help in cell division
Short hairs on the outside of
the cell for movement
(locomotion). Made of
microtubules and
microfilaments.
Long tail on the outside of a
cell for movement
Plant cells only
Cell wall
Chloroplast
Lysosome
Centrioles
Cilia
Flagella
Plant cells ,
fungus and
bacteria
Animal cells only
Animal cells only
Animal cells only
Animal cells only
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Prokaryotic cells
 Bacterial cells
 Much smaller and simpler than eukaryotic cells
 Organelles include only
o a plasma membrane
o cell wall
o capsule: extra protective layer outside the cell
wall
o ribosomes
o single loop of DNA free in the cytoplasm
o sometimes has pili: small hairs on the outside of
the cell used for movement
o sometimes has a flagella
DNA
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The Plasma Membrane
 controls what enters and leaves the cell
 maintains homeostasis (balance in the cell)
o Allows water, oxygen, and glucose to enter when
there’s not enough
o Allows water, carbon dioxide, and waste to leave when
there’s too much
 selective permeability: the membrane allows some
molecules, but not all, to pass through (semi-permeable)
 Made up of a molecule called a phospholipid
o lipid with a phosphate group
Charged and likes
to be near water
Hydrophilic
Uncharged and does not like
to be near water
Hydrophobic
 Plasma membrane is a phospholipid bilayer
o 2 layers of phospholipids back-to-back
o Polar heads face the water inside and outside the cell
o Nonpolar tails hide from water inside the membrane
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 In between the phospholipids in the plasma membrane,
there are
o proteins
 transport proteins: move needed materials or
waste across the cell membrane
o cholesterol: acts a glue to keep cell more rigid
o carbohydrates: attached to proteins to identify the
cell.
 Fluid mosaic model of the plasma membrane
o the membrane is fluid because the phospholipids are
constantly moving over the cell
o the proteins in the membrane are carried around by
the phospholipids, forming different mosaics
(patterns)
Why are viruses considered non-living?
* They can’t reproduce on their own. Need a host cell
to reproduce.